*{
    padding: 0;
    margin: 0;
}

.fl{
    float: left;
}

.first{
    background-color: #f00;
    width: 100px;
    height: 100px;
    border: 5px solid #000;
    margin-right: 10px;
    box-sizing: border-box;
}

.second{
    background-color: #ff0;
    width: 100px;
    height: 100px;
    border: 5px solid #1f6;
    
    box-sizing: border-box;
}